Method for separating alkali metal ions from alkoxylates

ABSTRACT

Alkali metal ions are separated off from alkoxylates containing alkali metal ions by a process comprising: 
     a) dilution of the alkali metal-containing alkoxylate with an inert solvent, 
     b) treatment of the alkali metal-containing solution of the alkoxylate with a cationic exchanger in order to obtain a substantially alkali metal-free solution of the alkoxylate, and 
     c) removal of the solvent from the substantially alkali metal-free solution of the alkoxylate in order to obtain a substantially alkali metal-free and substantially solvent-free alkoxylate.

The present invention relates to a process for separating alkali metalions from alkoxylates containing alkali metal ions, alkali metal-freealkoxylates and a process for the preparation of alkali metal-freealkoxylates.

Alkoxylates, in particular polyalkylene oxides and adducts of alkyleneoxides with alcohols and/or alkylphenols, are usually prepared underalkali metal hydroxide catalysis. Depending on the intended use, it isfrequently necessary to remove the catalyst as completely as possiblefrom the adduct. This is the case, for example, with alkoxylates whichare used as fuel additives or carrier oils in fuel additive packets orformulations. Such alkoxylates for carrier oils are in general adductsof propylene oxide and/or butylene oxide with alcohols and/oralkylphenols of more than 6 carbon atoms, which are prepared bycatalysis using potassium hydroxide. In order to ensure substantiallyresidue-free combustibility of the carrier oils, the catalyst must beseparated off. In the conventional processes, this is done byneutralization and precipitation as acidic potassium phosphate andsubsequent filtration. After the synthesis of the alkoxylates, alsoreferred to here generally as polyethers, it is therefore necessary toneutralize the potassium alcoholate contained in the product with dilutephosphoric acid (stoichiometric amounts of phosphoric acid dissolved inabout 10%, based on the reactor content, of water) and to distill offthe water for crystallization of the acidic potassium phosphate. Thereactor content must then be filtered, for example through a batchwisesheet filter, which is manually loaded and scraped off. Further requiredsteps are the separation and separate packing of product-moist salt andimpregnated filter sheets, their transport and incineration; thecleaning of the reactors before the subsequent batch, also in the caseof a batch procedure, in order to remove remaining phosphate residueswhich neutralize marked amounts of catalyst and can thus delay or evensuppress initiation of the oxyalkylation reaction; the drying of thereactors for the subsequent batch. It is clear that the removal of thecatalyst is expensive. Moreover, the carrier oils thus obtained stillcontain small amounts of potassium and also phosphorus, so thatresidue-free combustion of the carrier oils is not possible.

It is an object of the present invention to provide alkoxylates whichare substantially free of catalyst impurities from the preparation.

It is a further object of the present invention to provide a process forthe preparation of alkoxylates which are substantially free of catalystimpurities from the preparation.

It is a further object of the present invention to provide a process forseparating the catalyst from alkoxylates, which permits substantialremoval of the catalyst from the product and preferably avoidscontamination of the product with phosphate.

We have found that this object is achieved by the novel process for theseparation of alkali metal ions from alkoxylates containing alkali metalions (in particular potassium and sodium ions), which comprises thefollowing steps:

a) dilution of the alkali metal-containing alkoxylate with an inertsolvent,

b) treatment of the alkali metal-containing solution of the alkoxylatewith a cation exchanger for exchanging alkali metal ions for hydrogenions in order to obtain a substantially alkali metal-free solution ofthe alkoxylate, and

c) removal of the solvent from the substantially alkali metal-freesolution of the alkoxylate in order to obtain a substantially alkalimetal-free and substantially solvent-free alkoxylate.

In the novel process for the preparation of alkoxylates, the alkoxylatesare initially prepared in a conventional manner, and the catalyst isthen removed by the novel process for separating off alkali metal.

The term alkali metal-free or substantially alkali metal-free means thatless than 5, preferably less than 1, ppm of alkali metal ions arepresent. The alkali metal-containing alkoxylate to be purified generallycontains from 5 000 to 100, in particular from 2 000 to 1 000, ppm ofalkali metal ions.

The term substantially solvent-free means that the alkoxylate contains<1 000, preferably <500, ppm of solvent.

The term alkoxylate includes pure substances as well as mixtures whichare obtained using different alkylene oxides and/or different alcohols.

The term alkoxylate includes polyalkylene oxides (polyethers) andalcohol- and/or alkylphenol-initiated polyethers. The polyether or thepolyether moiety of the alcohol- and/or alkylphenol-initiated polyethersis generally composed of at least one C₂-C₆-alkylene oxide, inparticular ethylene oxide, propylene oxide, n-butylene oxide,2,3-butylene oxide and/or isobutylene oxide. In general, at least oneC₁-C₅₀-alkanol, preferably C₂-C₂₀-alkanol, particularly preferablyC₆-C₁₄-alkanol, in particular 2-ethylhexanol, nonanol, isononanol,tridecanol, isotridecanol, etc., is used as the alcohol. The alkylphenolused is in general a C₁-C₅₀-alkylphenol, particularly preferably aC₆-C₁₄-alkylphenol, preferably a C₆-C₁₄-alkylphenol, in particularnonylphenol, octylphenol or dodecylphenol, or a di-C₁-C₅₀-alkylphenol.

Alkanol-initiated polyethers having from about 10 to 35, preferably fromabout 15 to 30, alkylene oxide units are preferred.

The preparation of alkoxylates is known per se. Polyether syntheses aredescribed, for example, in Ullmann's Encyclopedia of IndustrialChemistry, 5th Edition, Vol. 21, 1992, 579-589, and the publicationsstated therein. The preparation of alcohol- or alkylphenol-initiatedpolyethers is described, for example, in Ullmann's Enzyklopädie dertechnischen Chemie, 4th Edition, Volume 22, 491-492 and Volume 19,31-33.

The catalyst-containing crude alkoxylate product is initially dilutedwith an inert solvent for removal of the catalyst. Solvents used are ingeneral an aliphatic or cyclic ether, such as tert-butyl methyl ether,tetrahydrofuran or dioxane, a hydrocarbon, such as pentane, hexane,toluene or xylene, a ketone, such as acetone or methyl ethyl ketone, andpreferably an alcohol, in particular a C₁-C₄-alkanol, such as ethanol,isopropanol, n-butanol, isobutanol and preferably methanol. For removalof the alkali metal catalyst, the dilute solution is treated with acation exchanger, for example is passed through an exchanger bed, inparticular in the form of a column, or is stirred with the cationexchanger. Particularly suitable cation exchangers are strongly acidic,macroporous resins, for example those based on crosslinked polystyreneshaving sulfonic esters as functional groups.

The amount of cation exchanger required for removal of the catalyst isdependent on the catalyst content of the product to be treated and onthe capacity of the ion exchanger used.

The solvent is then removed again, for example by distilling off. Theremoval is preferably effected in two steps. In a first step, the mainamount of the solvent is removed, preferably by distilling off, analkoxylate solution depleted of solvent and the solvent being obtained.In the first step, preferably at least 80% and up to 95% of the solventare removed. In a second step, the remaining amount of the solvent isremoved, preferably by stripping the depleted solution of the alkoxylatewith inert gas in a column, in order to obtain a substantially alkalimetal-free and substantially solvent-free alkoxylate and alcohol.

After a specific operating time, the cation exchanger needs to beregenerated. The regeneration is preferably integrated in the overallprocess, i.e. alkoxylate solution still contained in the cationexchanger is recovered before the regeneration and is recycled to stagec) or a) of the catalyst separation process. Any residues of thealkoxylate solution which still adhere to the cation exchanger areremoved by washing with the inert solvent. The wash solvent is likewiserecycled to stage a) of the catalyst separation process.

The regeneration of the cation exchanger preferably comprises thefollowing steps:

d1) removal of the alkoxylate solution from the cation exchanger and, ifrequired, washing of the cation exchanger with the inert solvent; thiscan be effected in such a way that the alkoxylate solution is removed,for example by discharging, and the cation exchanger is then washed withthe solvent; alternatively the solvent can be fed in without priorremoval of the alkoxylate solution, until the alkoxylate has been washedout,

d2) if required, washing of the cation exchanger with demineralizedwater,

d3) regeneration of the cation exchange resin with an acid, preferablysulfuric acid,

d4) washing the cation exchange resin neutral with demineralized water,

d5) washing out the water present in the ion exchanger resin with aninert solvent, preferably a water-miscible inert solvent, and

d6) if required, loading of the cation exchanger with the inert solventdesired for the treatment with the cation exchanger.

The inert solvent used in the regeneration of the cation exchanger ispreferably the same as that also used in the catalyst separationprocess. Step d6) is then omitted.

Preferably, the alkoxylate adducts are stripped with steam or an inertgas, such as nitrogen, after the synthesis, i.e. before step a) of thenovel process.

The present invention can be particularly advantageously used forseparating potassium ions from adducts of ethylene oxide and/orpropylene oxide and/or butylene oxide, in particular propylene oxideand/or butylene oxide, with C₆-C₁₄-alcohols and/or C₆-C₁₄-alkylphenols,the inert solvent used preferably being a C₁-C₄-alkanol, in particularmethanol.

A preferred embodiment of the present invention is described below. Thestated amounts of solvent/diluent and temperature ranges are preferredvalues for separating potassium from propylene oxide/butylene oxideadducts using methanol as a diluent. They may assume different values inthe case of other adducts, catalysts and solvents, but the optimumvalues can be readily determined by a person skilled in the art usingroutine methods.

For dilution of the potassium-containing adduct (step a), preferablyfrom 5 to 25, particularly about 15, % (m/m) of methanol are added tothe adduct. The methanolic solution is then treated with a cationexchanger, for example is passed over an ion exchanger bed whichcontains a cation exchanger. It is possible to use a commercial ionexchange resin, preferably in granular form. For example, theabovementioned ion exchangers, for example Lewatit SP 120 (Bayer) andAmberlite 252 C (Rohm and Haas), are suitable.

The service life of the cation exchanger is in general 1 year or longer.On passing through the ion exchanger, the methanolic solution ispreferably at from about 20 to 60° C., particularly preferably about 50°C. The cation exchanger is present in the acidic form. During thepassage of the potassium-containing methanolic solution of the adduct itbinds potassium ions and releases protons according to the followingequation:

R—O—(CHR′—CHR″—O)_(x)—K++IEXH+R—O—(CHR′—CHR″—O)_(x)—H++IEXK+

IEX=ion exchanger

R=alkyl or alkylaryl

R′═R″=H, CH₃, C₂H₅

After the treatment with the cation exchanger, the methanolic adductsolution is greatly depleted of potassium, in particular substantiallypotassium-free, and particularly preferably the concentration of thepotassium ions is not more than 1 ppm.

For separating off possible fine fractions of the ion exchange resin,the solution is then filtered in a conventional manner. Before thefurther treatment, it may be temporarily stored in a container.

It is advisable for the potassium content of the adduct solution leavingthe ion exchanger to be monitored continuously or at least at regularintervals by means of analytical measurement. In the event of abreakthrough of potassium ions the exchanger must be regenerated. Thisis done by means of an acid, preferably sulfuric acid, particularlypreferably about 5% strength sulfuric acid, by the following procedure:

First, the feed stream of the potassium-containing methanolic solutionof the adduct to the ion exchanger is stopped. Then, methanol can be fedin in order to wash the ion exchanger product-free. Adduct-containingmethanol, which in turn is used for diluting the crude product, i.e. thecatalyst-containing alkoxylate, is obtained. However, before the washingwith methanol, the potassium-free adduct solution still present in theion exchanger is preferably forced out of the ion exchanger withnitrogen or another inert gas and is combined with the otherpotassium-free adduct solution for the further treatment. The ionexchanger is then washed product-free with methanol, and the washmethanol leaving the ion exchanger and containing a small amount ofadduct is used for diluting the potassium-containing crude product.Preferably, the wash or rinse methanol is also preferably filtered toseparate off possible fine fractions of the ion exchange resin beforebeing used further.

The potassium-laden ion exchanger is now full of methanol, which has tobe removed before the regeneration. One possible method is to wash theion exchanger with demineralized water by the countercurrent orcocurrent method. The methanol-containing wastewater obtained here isnot used further but is disposed of via a wastewater treatment plant. Inorder to avoid relatively large losses of methanol, it is, however,preferable to remove the methanol, for example to force it out of theion exchanger by means of an inert gas, such as nitrogen, before washingthe ion exchanger with demineralized water. This methanol is preferablycombined with the other, adduct-containing rinse methanol and is usedagain for diluting subsequent batches of potassium-containing adducts.

The ion exchanger is then converted back into the acidic form by passingthrough dilute sulfuric acid (1 to 20% by weight), preferably about 5%strength sulfuric acid, by the countercurrent method. This is followedby washing neutral with demineralized water, and the water is finallywashed out with methanol, preferably by the trickle-bed procedure. Theresulting aqueous methanol phase can be used instead of fresh methanolfor preliminary cleaning of reactors on product change.

After complete replacement of the water by methanol, the ion exchangeris ready for operation again and can be loaded again.

The substantially potassium-free adduct solution leaving the ionexchanger is further treated as follows:

For reasons relating to application technology, the solution must befreed from the solvent as completely as possible. This is preferablycarried out in an evaporator unit, in particular a single-stage one,with connected stripping column. The preferred temperature range is fromabout 150 to 170° C., particularly preferably 160° C. First, the mainamount of the methanol, preferably at least 80%, is separated off bydistillation. The recovered methanol can be collected and reused.

In particular an inert gas stripping column in which the concentrationis reduced to methanol contents of less than 1 000 ppm, preferably lessthan 500 ppm, is used for removing the remaining methanol from theadduct solution. The inert gas is preferably nitrogen.

The methanol stripped off in the stripping column can also be reused.The substantially potassium-free desired products having a low methanolcontent and leaving the stripping column are preferably passed through aheat exchanger, where they preheat the adduct solution having a lowpotassium content, before entry into the evaporator apparatus and arethemselves cooled to about 50 to 60° C.

The novel process comprises a plurality of process steps in which puremethanol is required, i.e. in washing the ion exchanger free of product,in washing the water out of the ion exchanger and in filling the ionexchanger with methanol after the regeneration and, if required, fordiluting the crude product prior to separating off the potassium in theion exchanger. The methanol distilled off and stripped off is preferablyreused for this purpose. For diluting the potassium-containing crudeproduct, adduct-containing methanol from the washing out of the ionexchanger is preferably additionally or exclusively reused.

In the drawings:

FIG. 1 shows a flow diagram of an ion exchange unit as used for carryingout the novel process and

FIG. 2 shows a flow diagram of an evaporator unit downstream of the ionexchange unit and intended for separating off the diluent methanol.

The invention is described in detail on the basis of a particularlypreferred embodiment with reference to the figures.

As can be seen in FIG. 1, the crude, potassium-containing,methanol-diluted alkoxylates (butylene oxide adduct with isotridecanol)are transported via the line 3 by means of the pump P20 over a cationexchanger bed 2 in the container 1. In the container, an ion exchangeresin is installed between two sieve plates. The ion exchanger isinitially present in acidic form and binds potassium ions with releaseof protons. The dilution of the alkoxylates with methanol is necessaryin order to achieve substantially complete cation exchange. Themethanol-diluted alkoxylates entering the container 1 have a temperatureof about 50° C.

The alkoxylate solution emerging from the container 1 via line 4 issubstantially potassium-free. It passes through the filter F10 forseparating off possible fine fractions of the exchange resin and is thentemporarily stored in the container 5.

By analytical measurement, the alkoxylate stream leaving the container 1is constantly monitored for freedom from potassium. In the event of abreakthrough of potassium ions, the exchanger must be regenerated. Thisis done using about 5% strength sulfuric acid by the followingprocedure:

The feed stream of the crude alkoxylate to the container 1 is stopped;the methanol-diluted alkoxylate still remaining in the exchangercontainer is then forced into the container 5 by means of nitrogen. Theion exchanger in the container 1 is then washed product-free withmethanol, which is transported from container 6 via line 7 with the pumpP21; the container 1 is then emptied again by forcing in nitrogen. Theresulting, alkoxylate-containing rinse methanol passes through thefilter F10 into the container 8 and is used again for dilutingsubsequent batches of the crude alkoxylates in the reactors of thesynthesis plant.

After replacement of the alkoxylate in the ion exchanger by methanol,the container 1 is emptied as completely as possible into the container8, and the ion exchange resin is then washed by the countercurrentmethod with demineralized water, which is fed in via line 9. Theresulting wastewater which still contains methanol in the initialfractions is disposed of via line 10.

After a pure water phase is present in the container 1, the regenerationof the laden ion exchange resin is carried out by passing through about5% strength sulfuric acid by the countercurrent method via line 11. Theion exchanger is converted back into the acidic form, and a dilutesolution of potassium sulfate, potassium bisulfate and sulfuric acidleaves the container 1 and is disposed of via line 10.

After complete regeneration, the ion exchanger fill is washed acid-freewith demineralized water via line 9, the container 1 is then againemptied as completely as possible and residual water is replaced bymethanol. The methanol required for this purpose is transported by meansof the pump P21 from the container 6.

The aqueous methanol phases obtained in this process step aretransferred via line 12 into the container 13 and temporarily stored andare used in the synthesis of the alkoxylates instead of fresh methanolfor preliminary cleaning of reactors on product change.

After complete replacement of the water by methanol, the ion exchangerin the container 1 is ready for operation again and can be loaded againwith methanolic alkoxylate solutions via the pump P20.

The methanol-containing and substantially potassium-free alkoxylatestemporarily stored in the container 5 are then freed as completely aspossible from the solvent.

This is done in a downstream single-stage evaporator unit withsubsequent nitrogen stripping column at about 160° C. (FIG. 2):

Substantially potassium-free alkoxylate solution is transported from thecontainer 5 by means of the pump P26 via line 14 into theforced-circulation evaporator 15, with which the evaporator reboiler 16is coordinated. The methanol is partially separated off by a procedurein which the vapor of the evaporator reboiler 16 is condensed in thecondenser 17 and is collected in the methanol container 6.

From the evaporator reboiler 16, the alkoxylated depleted of methanoland at about 160° C. is fed to the top of the column 18 and is strippedcountercurrently with nitrogen, which is fed in via line 19.

The waste gas leaving the column 18 via line 20 is disposed of afterseparating off condensable fractions (methanol), which are likewisecollected in the container 6.

From the bottom of column, substantially methanol-free alkoxylate istaken off via line 21 and is used or stored.

The novel ion exchange process has the following advantages over thephosphate precipitation process of the prior art:

After the synthesis of the alkylene oxide adducts with alcohols bycatalysis with potassium hydroxide, a number of process steps areomitted:

neutralization of the potassium alcoholate with dilute phosphoric acidand distilling off the water for crystallization of the acidic potassiumphosphate,

filtration of the reactor content through a batchwise sheet filter whichis manually loaded and scrapped off,

separation and separate packing of product-moist salt and impregnatedfilter sheets and transport for residue incineration,

cleaning of the reactors before the subsequent batch, also in the batchprocedure, in order to remove remaining phosphate residues whichneutralize marked amounts of catalyst and can thus delay or suppressinitiation of the oxyalkylation reaction,

drying of the reactors for the subsequent batch, in the novel process incombination with the catalyst preparation of this lot.

The novel process permits economically and environmentally friendlypurification of alkoxylates, in particular of carrier oils, at least toproducts of high quality. The novel ion exchange process gives carrieroils which undergo combustion without residues in the engine and have noemissions of additional foreign substances. Moreover, the novel processpermits a capacity increase, which is substantially due to the fact thatthe reactors are available exclusively for the process of the synthesisof the alkylene oxide adducts.

We claim:
 1. A process for separating alkali metal ions from alkoxylatescontaining alkali metal ions, comprising: a) dilution of the alkalimetal-containing alkoxylate with an inert solvent for the alkoxylate toform a solution, b) treatment of the alkali metal-containing solution ofthe alkoxylate with a cationic exchanger comprising a cation exchangeresin in order to obtain a substantially alkali metal-free solution ofthe alkoxylate, and c) removal of the solvent from the substantiallyalkali metal-free solution of the alkoxylate in order to obtain asubstantially solvent-free alkoxylate containing less than 5 ppm alkalimetal ions, which process includes a regeneration of the cationexchanger, the regeneration comprising the following steps: d1) removalof the alkoxylate solution from the cation exchanger and washing out thecation exchanger with an inert solvent, which inert solvent has the capability of forming a solution of the alkoxylate, d2) optionally washingout the cation exchanger with demineralized water, d3) regeneration ofthe cation exchange resin with an acid, d4) washing the cation exchangeresin neutral with demineralized water, d5) washing out the waterpresent in the ion exchange resin with an inert solvent and d6)optionally loading of the cation exchanger with the inert solventdesired for the treatment with the cation exchanger, wherein in step d1)the alkoxylate solution is removed from the cation exchanger by forcingit out by means of an inert gas.
 2. A process as claimed in claim 1,wherein the removal of the solvent is effected in two steps, whereinfirstly c1) the main amount of the solvent is removed in order to obtainan alkoxylate solution depleted of solvent and then c2) the remainingamount of the solvent is removed from the alkoxylate solution depletedof the solvent, in order to obtain a substantially alkali metal-free andsubstantially solvent-free alkoxylate.
 3. A process as claimed in claim2, wherein the solvent is distilled off in step c1) and/or the remainingamount of the solvent is removed by stripping with inert gas in stepc2).
 4. A process as claimed in claim 1, wherein the alkoxylate is anadduct of ethylene oxide and/or propylene oxide and/or butylene oxidewith at least one C₁-C₅₀-alkanol and/or at least one (C₁-C₅₀-alkyl)phenol.
 5. A process as claimed in claim 1, wherein the alkali metalions to be separated off are potassium ions.
 6. A process as claimed inclaim 1, wherein the solvent used for diluting the alkoxylate and/or inthe regeneration of the cation exchanger is a C₁-C₄-alkyl alcohol.
 7. Aprocess as claimed in claim 1, wherein, in step b), an alkoxylatesolution having an alkali metal content of not more than 1 ppm isobtained.
 8. A process as claimed in claim 6, wherein the solvent ismethanol.